The invention relates to a method for transferring data from a first switch to a second switch, selectively by line switching or by packet switching, and to a switch for carrying out the method.
The present-day situation in telecommunications is marked by a division between two different connecting and switching technologies. These are the synchronous line-switching technology (line-switching or circuit switching) and asynchronous packet-switching technology (packet-switching).
Line-switching connections use line switches, alias line switching equipment, between the individual line sections, each of which copies over 1 byte packets and has a corresponding buffer size. Packet-switching connections use packet switches, alias packet switching equipment, between the individual line sections of a network, each of which copies over multi-byte packets. The buffer size of a packet switch correspondingly amounts to n bytes where n stands for the number of bytes in the copied data packets. The term “switch” is used below so that it includes both a line switch of a line switching network and a packet switch of a packet switching network.
A line switch, alias line switching equipment, is called telecommunications apparatus (TK apparatus) in the private sector, and exchanges of the network supplies in the public sector. A packet switch, alias packet switching apparatus, is also called a router, an IP switch or a host computer.
Line switching connections are synchronous, i.e., data transfer is carried out substantially without any time delay from one line section to an adjoining line section through a switch (here, a line switching apparatus).
When a line-switching call is put through, a connection is continually provided in real time with the complete bandwidth of a channel between two points. Even if no useful information is being sent e.g., during a pause in telephone conversation, the transmission channel is occupied or engaged. Line-switching connections are expensive, particularly during telephone conversations since the costs accumulate irrespectively of the information actually transferred. The advantage of a line switching connection is that it is free of any time delay and has a fixed bandwidth.
The other important type of data exchange nowadays is the packet exchange. With packet exchange, data, e.g., audio data, video data or computer files, are packeted and transferred as data packets. Packet switching works in the asynchronous transfer mode, i.e., data is transferred time-delayed between two adjoining line sections by a switch (here, a packet switching apparatus). In the case of packet-switching exchanges, and quite differently from line-switching exchanges, a fixed connection does not have to be maintained. It is connection-less, i.e., each packet is treated individually and not in conjunction with others.
Packet switching is used in particular on the Internet. The data packets are termed there as IP packets (IP=Internet Protocol). Each IP packet contains a header which contains, inter alia, sender and receiver addresses. The IP packets form a data flow which is transferred through packet switching apparatus (alias IP switches or Routers or Host computers) in the Internet from the sender to the relevant receiver.
As a result of the length of the IP packets (16 bytes or more), a time delay occurs in the packet switching apparatus when copying. This time delay can be so great, when there is a heavy load on the packet switching apparatus which passes a data packet over the route to the destination address, that certain applications are no longer possible.
These delays are of considerable significance particularly in the case of the Internet. With Internet telephony, a cost-conscious caller uses the normal Internet with approximately 8 kbit/s bandwidth and a time delay of 0.5 seconds. When the Internet is overloaded, the time delay of the individual packets becomes so great that an acceptable conversation connection between telephone partners is no longer possible.
Internet telephony is marked by a great advantage that only the relevant local telephone charges to the next POP (Point of Presence), the access point to the Internet offered by an Internet Service Provider ISP, as well as time charges calculated by the ISPs for the length of the Internet access as well as volume charges, but not expensive long distance telephone charges are incurred.
From U.S. Pat. No. 4,996,685 a method and device are known which allow in an ISDN communications network, during an existing connection between a user and a host computer, a dynamic change between a line switching connection through an ISDN B channel and a packet-switching connection through an ISDN D channel. A command to change between a line-switching and a packet-switching connection thereby always emanates from the Host computer.
The method disclosed in U.S. Pat. No. 4,996,685 is restricted to undertaking on an ISDN connection a change between a line-switching and a packet-switching data transfer whereby a line-switching transfer is carried out on a B channel and a packet-switching transfer is carried out on the D channel. A method of this kind is indeed expedient to produce effective access from an end subscriber to a host computer, possibly an exchange point of the telephone network or an access point to the internet, but does not relate to the transfer of data between switches or routers of a network.
WO 95/31060 A1 describes a method for transferring data between an information source and a destination device wherein the data to be transferred are transferred as data packets. Depending on type of information of the data packets, the data are transferred automatically either solely by line-switching or solely by packet-switching. More particularly in the case of small amounts of data to be transferred, a packet-switching transfer is chosen and in the case of large amounts of data, a line-switching data transfer is chosen.
WO 95/25407 A1 describes a method for transferring data between a data source and transceiver either through a packet-switching network or a line-switching network. A control device is thereby provided which uses certain criteria to decide which network and which method of transfer is best suited for the transfer and then selects same.
U.S. Pat. No. 4,903,260 describes a digital coupling network and a coupling field chip which are designed so that paths leading from any input to any output can, depending on requirements, either be switched through for line-switching connections or can be preset for packet-switching information. Preset paths for the packet-switched information thereby form a network whose junctions lie in the coupling field chip of the coupling network. Those function devices which are required to send each data packet on the path preset for same are integrated in the coupling field chips. It is thus possible to divide up a single coupling network depending, on requirements, dynamically into a line-switching network and a packet-switching network.